1. Field of the Invention
The invention relates to air brakes and more particularly to an improved spring guide mechanism for the type of safety brake which does not require fluid pressure for activation.
2. Description of the Prior Art
Pneumatic operated brake systems are widespread, especially in the trucking industry. Applicant has been active in the field of safety brake mechanisms and U.S. Pat. Nos. 3,101,219, 3,244,079 and 3,439,585 are illustrative, both of applicant's contributions and what are believed to be the most advanced safety brake mechanisms available.
There is normally provided in combination with the conventional fluid pressure operated brake, an automatically operated safety or parking brake mechanism which is normally subjected to the same air pressure as is employed for operating the brake. Such air pressure is sufficient to maintain the auxiliary safety mechanism in its inoperative position. In the event of failure of the compressed air supply or reduction in pressure below a pre-selected value, a spring mechanism automatically operates to apply the brake and to hold it in the applied position until the air pressure is restored to its normal value. When the vehicle is parked and the air pressure is reduced or turned off entirely, the auxiliary mechanism operates automatically to apply the brakes until the air pressure is again brought up to the desired value. Further, when the vehicle is in operation and moving, a loss of air pressure will cause the auxiliary mechanism to automatically apply the brake and thus provide a safety feature.
The automatically operated auxiliary safety mechanism comprises a reciprocal plunger which is actuated in response to motion of a diaphragm produced by a compression spring, i.e., the barrel spring, against one side of the diaphragm. Normally, the same fluid pressure which operates the brake is applied against the opposite side of the diaphragm and maintains the barrel spring under compression and inoperative. Upon a loss or failure of pressure, the barrel spring causes displacement of the diaphragm and plunger and corresponding movement of the conventional brake mechanism, including the brake rod, to apply the brake.
The mentioned auxiliary safety mechanisms, as described above and as further illustrated in the mentioned prior patents, while representing an advance in the art, have not proven entirely satisfactory. For example, under some conditions of overhaul and maintenance, a premature release of the auxiliary safety mechanism plunger and its associated, exceptionally strong barrel spring has occurred resulting in physical damage and injury. Also, the plunger of the safety mechanism, after extended service, has become wobbly and the barrel spring has sometimes been allowed to assume a cocked position within the housing which prevents proper function of the brakes. Also, the prior art mechanisms have inherently introduced physical structure on the top housing surface which has presented an obstacle, both to maintenance and operation.
With the foregoing in mind, the present invention is primarily directed at providing an improved telescoping sleeve arrangement for the barrel spring so as to provide an overall safer type of safety brake mechanism particularly for maintenance and overall purposes and also to provide a flat obstacle-free top housing surface.